Characteristics of transmission fibers, e.g., fiber loss and dispersion, may change over time, and there is often a need for operators of optical communication network, e.g., wavelength division multiplexing (WDM) systems, to obtain updated information on span length, span loss and fiber dispersion between communication nodes or network elements (NE) in deployed systems.
Optical time domain reflectometry (OTDR) is typically used for determining fiber characteristics during initial calibration of a transmission fiber. Using the OTDR device, fiber characteristics can be derived by sending a pulse of light down the fiber and measuring its back reflection. Based on the optical power received, the length of time to receive the reflected signal, and the phase shift of the signal, an approximation of the fiber length, residual chromatic dispersion, and fiber loss can be obtained. One drawback in such a technique is that, once the fiber is connected to a WDM system and deployed in the field, OTDR measurements cannot be performed without interfering with live traffic, including for example, disconnecting the transmission fiber from the WDM system.
Alternative methods for fiber characterization in WDM systems are thus needed.